Regeneration of the periodontal tissues lost due to periodontal disease is one of the most important objectives of periodontal therapy. The progenitor cells for the formation of a new connective tissue attachment on a previously diseased root surface are believed to be located in the underlying healthy periodontal ligament (PDL). Currently-available therapeutic procedures do not result in the much desired new connective tissue attachment because the rapid apical migration of the oral epithelium along the root surface prevents the coronal migration of the progenitor cells. Recent experimental studies (Nyman et al'82; Aukhil et al'83) suggest that the chances of obtaining a new connective tissue attachment may be enhanced if a "periodontal space" is created to allow coronal migration of the progenitor cells. Creating such a "periodontal space" does not, however, mean that only the progenitor cells from the PDL populate the curetted root surface. It is possible that cells from the crest of the remaining alveolar bone may also be populating the curetted root surface. The specific aim of the proposed research is to study, using autoradiographic techniques, the exact source of cells that first populate the curetted root surface when a' periodontal space' is created in experimental periodontal wounds. This important information is necessary to design surgical techniques aimed at regeneration of periodontal tissues lost due to disease. Incisors and premolars will be extracted in monkeys and incubated for one hour in culture medium (MEM) containing [3H]-thymidine inorder to label the remaining viable PDL cells on the root surface. While the cells on the root surface are being labelled, windows of standard dimensions will be prepared in the buccal cortical plates of sockets of these teeth. The teeth with labelled PDL cells on their root surfaces will then be replanted in their sockets. The PDL, cells and cementum from that portion of the replanted tooth which is now exposed in the window will be removed using round burs at slow spped. The wounds will be covered with millipore filters and the flaps will be replaced and sutured. The monkeys will be sacrificed to give observation periods of 24, 48 and 96 hours. The specimens will be processed (autoradiography) and the kinds of cells (labelled/unlabelled) that have populated the curetted root surface will be examined. Consideration will be given to the kind of cells that first populate the curetted root surface when a "periodontal space" is created in experimental periodontal wounds.